It kind of depends what your washing off of them. Hot water will help take off tough grease and caked on food better than cold. The extra heat also helps kill germs if you're washing something meat has come in contact with. However, if you ate a veggie sandwich off a plate and there's just a little crumbs on them, or your washing a glass you just drank some juice out of, I doubt it would hurt to wash them in cold water. However, if your washing the cutting board you just used to cut up steaks on, or a glass from last night you drank milk out of, you really should use hot water and an antibacterial soap to clean them.